In order to improve a level of performance of a safety equipment such as a seatbelt, an air-bag or the like, an actuation of the safety equipment may be controlled in accordance with a weight of a passenger sitting on a vehicle seat to which the safety equipment is provided. For example, when a passenger sitting on the seat does not fasten the seat belt, the passenger is generally notified of not wearing the seat belt by an alarm or warning. The law in the United States states that, when an adult is sitting on a passenger seat, an air-bag must be deployed in the event of a vehicle collision or the like. On the other hand, the law also states that, when a passenger such as a baby or a child is placed in a child seat fixed on the passenger seat in a manner where the occupant of the child seat faces the seat back of the passenger seat, the air-bag must not be deployed because an impact caused by the deployed air-bag may cause damage to the occupant of the child seat in the event of a car accident. A determination that the passenger sitting on the passenger seat is an adult, is executed on the basis of a value of a weight of an adult female whose weight is relatively light and height is relatively low. A determination that the passenger sitting on the passenger seat is a child, is executed on the basis of a suitable basis. Thus, in view of safety matter, it is important to determine a type of passenger on the basis of a weight of the passenger.
Disclosed in JPH9-207638A is an occupant detecting apparatus for determining an existence of an occupant of a seat by detecting a load acting on the seat. The occupant detecting apparatus includes two load sensors that are provided at two of four seat attaching portions, and the existence of the occupant is determined on the basis of a total of load value detected by the two load sensors. Accordingly, the occupant detecting apparatus includes the load sensors provided at two of four seat attaching portions, where the two portions are a necessary minimum to determine the existence of the occupant of the seat, thereby achieving a simple configuration and low cost occupant detecting apparatus.
Further, disclosed in JP3991740B is an occupant detecting apparatus for determining whether an occupant sitting on the seat is an adult or a child. The occupant detecting apparatus includes first and second load sensors for respectively detecting a load applied to the seat in the vicinity of the buckle of a seat belt and a load applied to the seat at a portion opposite to the buckle of the seat belt, detecting means for detecting an insertion of a tongue plate into the buckle, determining portion for determining the occupant to be an adult in a case where a total of the load values detected by the first and second load sensors are equal to or more than a threshold that is set in advance. Further, the determining portion determines the occupant to be a child in a case where, even when the total of the load values is equal to or more than the threshold, a difference between the load value detected by the first load sensor and the load value detected by the second load sensor has increased to be a predetermined value or more, and the load value detected by the first load sensor has increased before and after a timing where the tongue plate is inserted into the buckle. In this configuration, an error in determination may be reduced, the error would happen in a case where a child whose weight is slightly lower than a threshold sits on the seat, and the seat belt is fasten by other passenger. According to the description of the JP3991740B, the occupant detecting apparatus includes two first load sensors and two second load sensors at four seat attaching portions, so that a total load may be calculated on the basis of the load values detected at four seat attaching portions (all of the seat attaching portions).
According to the occupant detecting apparatus disclosed in JPH9-207638A, the apparatus determines the existence of the occupant of the seat, however, because the apparatus includes a minimum number of the load sensors in view of achieving a cost reduction and a weight reduction, the apparatus may not be able to determine whether an occupant is an adult or a child.
As is the configuration of the occupant detecting apparatus disclosed in JPH9-207638A, where the load sensors are not provided at all of the seat attaching portions and provided at only two of the seat attaching portions, because the load value detected by the load sensor may change depending on a height of a seating surface of the seat and a vehicle tilt angle, a difficulty exists in determining whether the occupant is an adult or a child on the basis of the set threshold. Further, in a case where the seat includes a lifter by which the height of the seating surface of the seat is adjusted upwardly or downwardly, the load value detected by the load sensor may vary depending on the height of the lifter; accordingly a further difficulty exists in determining whether the occupant is an adult or a child.
According to the occupant detecting apparatus disclosed in JP3991740B, although the determination whether the occupant is an adult or a child (an infant) is executed with high accuracy by eliminating the effect of the load value temporally increasing at the time of the seatbelt fastening operation, because the apparatus includes four load sensors provided at four seat attaching portions, a cost and a weight of the apparatus would be increased.
A need thus exists to provide a seat occupant determining apparatus, which is not susceptible to the drawback mentioned above.